The present invention relates to curable compositions and more particularly to low VOC (volatile organic component) ambient temperature curable coating compositions containing low viscosity imine reactive diluents, which are especially suited for use in automotive refinish applications.
Due to increasingly stringent environmental regulations and the demand for better performance, reactive diluents/oligomers are becoming crucial components in a variety of automotive coating formulations. This is especially true for high solids coatings. Such products are typically enamels because low molecular weight building blocks can be used to form cross-linked networks that provide robust films. The rate of cure is therefore important since the rate of film formation determines autobody shop throughput and profitability. Certain imines and imine-containing coating compositions are known. Representative disclosures can be found in U.S. Pat. No. 5,198,524, U.S. Pat. No. 3,668,183, U.S. Pat. No. 4,772,680 and U.S. Pat. No. 5,288,802. None of these publications discloses the imines of this invention nor coatings that contain them characterized by low volatile organic content (VOC), good sprayability, quick cure and hard, solvent-resistant films formed therefrom.
The present invention is directed to an imine reactive diluent of Formula I: 
wherein
R and R1 are the same or different, and are independently selected from the group consisting of hydrogen, a C6 to C50, preferably C6 to C6 to C14, more preferably C6 to C8 aromatic structure, C1 to C50 alkyl moiety having a linear aliphatic, branched aliphatic, or cycloaliphatic structure. When the alkyl moiety has the cycloaliphatic structure it preferably includes 6 to 14 carbon atoms, when it has the linear or branched structure it preferably includes 1 to 10 carbon atoms.
R2 and R3 are the same or different, and are selected from the group consisting of a C1 to C50, preferably C1 to C10, more preferably C1 to C5 linear aliphatic, branched aliphatic, and cycloaliphatic structure. When R2 and R3 have the cycloaliphatic structure they preferably include 6 to 14 carbon atoms, when they have the linear structure they preferably include 2 to 10 carbon atoms and when they have the branched structure they preferably include 3 to 10 carbon atoms.
Y is a residue with a weight average molecular weight up to about 100,000, preferably 14 to 100,000, more preferably 14 to 50,000, most preferably 28 to 20,000 and having said linear aliphatic, branched aliphatic, cycloaliphatic, aromatic structure, or a combination thereof;
wherein R1,R2,R3 and Y are free from a hydrogen bonding group; and
x is an integer of at least 2, preferably 2 to 50, more preferably 2 to 10 and most preferably 2 to 4. Preferred imine reactive diluents of Formula I are those in which R and R1 are not both isopropyl.
R2, R3 or Y of the imine reactive diluent of Formula I may include one or more heteroatoms, preferably 1 to 3 heteroatoms in R2 and R3, and preferably 1 to 30 in Y. Preferred heteroatoms include O, S, Si and P but not N. To achieve good coating solution viscosity, there will be no hydrogen atoms on any of the heteroatoms.
The imine reactive diluent 1 is a ketimine when R and R1 are not hydrogen and an aldimine when R1 is not hydrogen.
Some of the preferred imine reactive diluent of Formula I include the following: 
Even more preferred imine reactive diluents of Formula I is:
I. A tetraketimine having the formula: 
II. A hexaketimine having the formula: 
III. An octaketimine having the formula: 
The imine reactive diluent of the Formula I is produced by reacting, in the presence of a Lewis acid catalyst and a reactive solvent, an acrylate group containing organic compound having the formula: 
with 1.0 mole of an imine reactant per mole of acrylate groups in the compound.
The organic compound may be obtained by conventional means, such as by reacting a polyol having the desired number of functionalities with an acryloyl chloride or acrylic acid. Typically, a free radical scavenger, such as monomethyl ether hydroquinone, generally at 50 to 100 ppm of the reaction mixture, is added to prevent undesired polymerization of the resulting acrylate groups.
The imine reactant may be obtained by first dissolving a corresponding amine compound which includes R2 and R3 functionalities into an excess amount of a reactive solvent, generally a ketone for producing a ketimine reactive diluent and an aldehyde for producing an aldimine reactive diluent. The reactive solvent contains the desired R and R1 functionalities. Some of the preferred ketones include acetone, methyl ethyl ketone, methyl pentyl ketone and preferably methyl isobutyl ketone. Some of the preferred aldehydes include propionaldehyde, butyraldehyde and isobutyraldehyde. The dissolved amine compound reacts with the reactive solvent at elevated temperatures to produce the imine reactant of the following formula: 
The imine reactant is then reacted with an organic compound having at least two acrylate groups to produce the imine reactive diluent. Depending upon the functionalities present on the imine reactant and the organic compound, the reaction is generally carried out at about xe2x88x9210xc2x0 C. to 100xc2x0 C., preferably, at about 0xc2x0 C. to 60xc2x0 C. and more preferably at about 15xc2x0 C. to 35xc2x0 C. in the presence of an excess amount of the reactive solvent. Typical Lewis catalyst suitably for use in the present invention is selected from at least one member of the group consisting of FeCl3, acidic gamma alumina, Yb(CF3SO3)3, Sc(CF3SO3)3, tetraisopropyl titanate, and La(CF3SO3)3. The amount of catalyst employable in the method of the present invention generally varies in the range of 0.01 to 20, preferably in the range of from 0.1 to 8 and more preferably in the range of from 3 to 7, all in weight percentages based on the weight of residue Y in the Formula I above. The applicants unexpectedly discovered a major improvement of the method of the present invention in that it permits one to produce the imine reactive diluent in the same reactor, without transferring the reaction mixture to any other reactors. The single reactor preparation makes the process simple-to-operate, safe and efficient.
The excess amount of the reactive solvent present in the reaction mixture is adjusted to provide a coating composition containing the imine reactive diluent of the present invention with a desired amount of VOC.
Specifically, an imine reactant may be obtained by dissolving diethylene triamine in an excess amount of 4-methyl-2-pentanone reactive solvent and then elevating the reaction mixture under reflux to about 142xc2x0 C. for producing the imine reactant of the following formula: 
Alternatively, the foregoing triamine-bisketimine may be obtained from Air Products of Allentown, Pa. Triamine-bisketimine (imine reactant) is then reacted in the same reactor, in the presence of a Lewis catalyst with an organic compound of the following formula: 
to produce the imine reactive diluent.
The present invention is also directed to a two-pack coating composition comprising a component (i) and a component (ii) wherein:
(i) comprises from 10 to 90, preferably 20 to 80 and more preferably 30 to 70 weight percent of an oligomer or a polymer having a weight average molecular weight not exceeding about 5,000, preferably 100 to 5,000, more preferably 200 to 4,500 and most preferably 300 to 4,000, and functionality selected from one or more of acetoacetate, acrylate, isocyanate, epoxide and cyclic carbonate moieties; and
(ii) comprises from 10 to 90, preferably 20 to 80 and more preferably 30 to 70 weight percent of an imine reactive diluent having a weight average molecular weight from about 100 to 100,000, preferably 200 to 100,000, more preferably 250 to 50,000 and most preferably 300 to 20,000, and that is substantially free of hydrogen-bonding moieties and contains at least three imine groups per molecule wherein all percentages are based on the total weight of said components (i) and (ii).
One example of the imine reactive diluent is of the following formula: 
The oligomer or polymer in the component (i) of the coating composition of the present invention are conventionally produced. A conventional acrylic polymer or oligomer, a polyester or a structured oligomer or polymer is reacted with compounds containing the desired functionalities, such as acetoacetate to produce the oligomer or polymer in the component (i). If desired the component (i) coating composition may further include a polymeric component (iii) selected from at least one of a polyacrylate, polyepoxide, polyurethane and polyester, the component having a weight average molecular weight between about 5,000 to 100,000, preferably 6,000 to 50,000 and more preferably 7,000 to 20,000, and a pendant functionality selected from at least one of acetoacetate, epoxide, isocyanate, cyclic carbonate, and acrylate moieties, the functionality comprising about 1 to 90 percent based on the weight of the monomer; the composition comprising from about 50:1 to 2, preferably 40:1 to 1:2, and more preferably 20:1 to 1:2, all by weight of said components (i+ii) to said component (iii). The polymeric component (iii) is prepared in a similar manner as to that described earlier for the oligomer or polymer used in the component (i).
The ratio of ketimine to acetoacetate, epoxide, isocyanate, cyclic carbonate, or acrylate moieties in the foregoing coating composition is in the range 5:1 to 1:5.
The foregoing coating composition preferably includes:
the component (i) comprising from 25 to 75 weight percent of the oligomer or polymer;
the component (ii) comprising from 25 to 75 weight percent of the imine reactive diluent; and
the component (iii) comprising from 1 to 50, preferably 2 to 40 weight percent of the polyester polyol or polyacrylic polyol.
In the foregoing coating composition the oligomer or polymer of the component (i) is functionalized with acetoacetate moieties;
the imine reactive diluent of the component (ii) is functionalized with ketimine moieties; and
the polyester polyol or polyacrylic polyol of the component (iii) is functionalized with acetoacetate moieties.
The present invention is also directed to a two-pack coating composition comprising a component (i) and a component (ii) wherein:
(i) comprises from 10 to 90 weight percent of an oligomer or a polymer having a molecular weight not exceeding about 5,000 and functionality selected from one or more of acetoacetate, acrylate, isocyanate, epoxide and cyclic carbonate moieties; and
(ii) comprises from 10 to 90 weight percent of an imine reactive diluent of Formula I described earlier.
If desired, The component (i) of the foregoing coating composition may further include the polymeric component (iii) described earlier.
The present invention is also directed to a method of producing a coating on a substrate comprising:
admixing the components (i) and (ii) of the coating composition described above to form a pot mix;
applying a layer of the pot mix on the substrate;
curing the layer to form the coating.
The inventors unexpectedly found that by including the highly reactive imine reactive diluents having low viscosity in a low VOC, high solids coating composition of the present invention, especially in an automotive refinish application, a layer from a pot mix of the containing composition can be readily applied by conventional means. Moreover, the layer dries at a very rapid rate, which is very important in an automotive, refinish environment.
Aldimine and ketimine reactive diluents having multi-imine functionality are disclosed. These highly reactive compositions are further characterized as having substantially no hydrogen bonding sites that can cause an undesirable increase in solution viscosities when employed as components of coating compositions. The imine reactive diluents of this invention (ketimines and aldimines) are characterized by the absence of hydrogen atoms on the nitrogen or oxygen atoms, which contributes to maintenance of good coating viscosities.
As used herein:
xe2x80x9cTwo-pack coating compositionxe2x80x9d means a thermosetting composition comprising two components that are stored in separate containers, which are typically sealed for increasing the shelf life of the components of the coating composition. The components are mixed just prior to use to form a pot mix, which has a limited pot life, typically a few minutes, such as 15 minutes to 45 minutes to a few hours, such as 2 hours to 6 hours. The pot mix is applied as a layer of desired thickness on a substrate surface, such as an autobody. After application, the layer dries and cures to form a coating on the substrate surface having desired coating properties, such as solvent resistance.
xe2x80x9cLow VOC coating compositionxe2x80x9d means a coating composition that is less than about 0.6 kilogram of organic solvent per liter (5 pounds per gallon) of the composition, as determined under the procedure provided in ASTM D3960. The amount of organic solvent used in the present invention results in the composition having a VOC of less than 0.6 kilogram (5 pounds per gallon) and preferably in the range of 0.012 kilogram to 0.528 kilogram (0.1 pounds to 4.4 pounds per gallon), more preferably in the range of from 0. 12 kilogram to 0.42 kilogram (1.0 to 3.5 pounds per gallon) of organic solvent per liter of the composition.
xe2x80x9cHigh solids compositionxe2x80x9d means a coating composition having a solids component of above 30 percent, preferably in the range of from 40 to 95 percent and more preferably in the range of from 45 to 80 percent, all in weight percentages based on the total weight of the composition.
xe2x80x9cGPC weight average molecular weightxe2x80x9d means a weight average molecular weight measured by utilizing gel permeation chromatography. A high performance liquid chromatograph (HPLC) supplied by Hewlett-Packard, Palo Alto, Calif. was used. Unless stated otherwise, the liquid phase used was tetrahydrofurane and the standard was polymethyl methacrylate. xe2x80x9cPolymer Solidsxe2x80x9d, xe2x80x9cBinder solidsxe2x80x9d or xe2x80x9cOligomer solidsxe2x80x9d means a polymer or binder or oligomer in its dry state.
xe2x80x9cStructured oligomer or polymerxe2x80x9d means a structured molecule, such as a macromolecule, oligomer or polymer, which unlike conventional resins, has a very well defined structure, such as star, expanded star, dendritic (hyper branched), or cyclodextrinic structured molecules.
xe2x80x9cHydrogen bonding groupxe2x80x9d means a group containing a heteroatom that is bonded to a hydrogen atom. For example, O, S or N.
xe2x80x9cResiduexe2x80x9d means a fragment that is a compound, oligomer or a polymer.
Imine Reactive Diluents
Representative imine reactive diluents of this invention are typically advantageously prepared in a single reactor by the following procedure. A three neck flask equipped with a magnetic stirrer, Dean-Stark trap and condenser, thermometer, oil heating bath and an Argon (Ar) inlet and outlet is charged with a triamine (0.50 mol) having two primary amine termini and an internal, aliphatic secondary amine group, and an aldehyde or ketone (1.22 mol) suitable for use in an imine-forming reaction. The solution is heated to reflux under Ar and water is removed azeotropically via the Dean-Stark trap. The mixture is cooled to room temperature and a reagent containing two, three or more acrylate groups is then added to the reaction flask wherein bis-ketimine to acrylate is about 1:1 by moles. The resulting mixture is stirred under Ar in the presence of a Lewis acid catalyst until residual acrylate in the reaction mixture is no longer detectable by 1H NMR spectroscopy. The product is then filtered under Ar to remove the catalyst.
Coatings
As referred earlier, the preferred coating compositions comprise from 25 to 75 weight percent of component (i), from 25 to 75 weight percent of component (ii), and 0 weight percent of component (iii), based on a total of 100 weight percent. Other preferred compositions have similar amounts of components (i) and (ii) but component (iii) will be present at 1 to 50, more preferably 2 to 40 weight percent. Specific preferred oligomers (i) are structured and unstructured polyesters and polyacrylics that contain pendant acetoacetate or acrylate moieties; preferred oligomers (ii) are of Formula 1 (wherein x=2, 3 or 4); and preferred polymeric components (iii) are polyesters and polyacrylics that contain acetoacetate or acrylate pendant moieties.
Representative coatings containing imines of this invention are generally prepared by combining the imines with complementary coating-formation ingredients that will be obvious to one having ordinary skill in this art.
The imine reactive diluents of this invention provide the following advantages over conventional materials:
(i) they are formed from unhindered amines, therefore reactive amine end groups are generated after unblocking (loss of ketone or aldehyde). This results in rapid reaction with electrophiles;
(ii) they are multifunctional (3 or more). This makes them orders of magnitude higher in reactivity than difunctional compounds; and
(iii) they do not contain H-bonding moieties and, as a result, provide dramatically lower solution viscosities at high solids (e.g., xe2x89xa765 percent wt. solids) and can be applied via conventional spray guns. This attribute is particularly important for low VOC coatings.
These imine reactive diluents contain all three of the attributes described above, while conventional imines are either difunctional and do not contain H-bonding moieties, which results in very slow reaction with electrophiles, or they are multifunctional but contain H-bonding moieties which precludes their use in high solids, low VOC coatings due to their high solution viscosities. The compositions of this invention are characterized by being quick-drying, having low solution viscosity, and cured films made from them have good solvent resistance.
The coating composition of the present invention may also contain conventional additives, such as pigments, stabilizers, rheology control agents, flow agents, toughening agents and fillers. Such additional additives will, of course, depend on the intended use of the coating composition. Fillers, pigments, and other additives that would adversely effect the clarity of the cured coating will not be included if the composition is intended to be used as a clear coating. The foregoing additives may be added to either the component (i) or the component (ii), or both, depending upon the intended use of the coating composition.